The present invention relates to a cut gem comprising a first predetermined number of facets cut in the crown and a second predetermined number of facets cut in the pavilion above a central geometric axis of symmetry.
For many centuries, gems were cut roughly, in cabochon or in various often irregular shapes, with the only concern to give to the gem the greatest volume possible. These ancient stones often were dull, without brilliance, even when they were beautifully polished. At present, the cutting technique has greatly evolved. The cut is executed scientifically by observing the laws of crystalline optics so as to obtain the best yield of optical qualities for transparent gems. It is sought particularly to give to the stones maximum brilliance, which is the case when they reflect externally the greatest part of the light that they receive. On the other hand, diamond has a high dispersion of index of refraction as a function of the wavelength of the light. The strong dispersion is the origin of the fire the diamond displays. It is to be noted that a sheet with parallel surfaces cannot show fire, nor can a stone returning white light by simple reflection without the light being broken up by refraction. There is fire only if the light is broken by refractions and reflections on the polished facets of the cut diamond. There have thus been developed xe2x80x9cbrilliantxe2x80x9d cuts that are more and more improved, as described for example in Swiss patent 684,301. These brilliant cuts have in general a fourway geometric axis of symmetry by placing the cut facets parallel to the generatrix of the cone which envelops them, that are four in number or multiples of four, such as eight stars, sixteen crown triangles and sixteen pavilion triangles. Diamonds thus cut return to the observer an image with a fourfold symmetry.
It is the object of the present invention to create a new gem cut permitting obtaining the original optical effects and a differently designed shape, whilst maintaining the intensity of the brilliance and fire of the non-brilliant cuts.
The gem, in particular the diamond thus cut, returns toward the observer an image having a generally hexagonal symmetry and a play of reflections of light and different colorations like six-rayed stars in which the lobes return toward the observer chatoyant optical effects.
According to a preferred embodiment, the gem is constituted by diamond or a stone having an index of refraction and a dispersion substantially equal to those of diamond.
With these characteristics, there are obtained particularly important optical effects of light play.
Preferably, its central axis of geometric symmetry corresponds to one of the ternary crystallographic axes of symmetry of the diamond.
This characteristic permits obtaining the facilitated and certain cut of the table by cleaving the diamond on one of the faces of the octahedron. Moreover, the quality of the cut of the facets can thus be predetermined and carried out with high precision.
The invention also relates to a process for cutting a gem, in particular a diamond, characterized by the fact that first of all, all the facets of the crown and of the pavilion are cut, and that then the lobed periphery of the girdle is cut out by forming the lobes in six portions with rounded projections and six portions with rounded hollows.